Genesis 43:20-22

‘And said, “Oh my lord. We did indeed come down at the first time to buy food, and it happened that as we came to the lodging place that we opened our sacks and behold every man's silver was in the mouth of his sack, our silver in full weight. And we have brought it again in our hand. And we have brought other silver down in our hand to buy food. We do not know who put the money in our sacks.”

The brothers are trying to summarise the story as quickly as possible before they are brought into the house, thus they have to abbreviate what happened. They remember vividly the moment that they first found the silver in one of the sacks and telescope what happened into a few scared, hurried words. Thus the finding of the silver in all the sacks is described as happening at the same time, although we know from earlier that that happened later when they arrived home. It is the primary point that they want to get home. They found the silver in their sacks. They have only a few moments, so detail is of secondary importance. Then they assure him earnestly that they have brought it back with other silver for new purchases.